Teeth

If you want a long range spell teeth is the spell to get but it is not a very good investment because teeth does very little damage in the long run and will end up as wasted skill points.

Bone Armor

Since the necromancer is one of the weaker characters in Diablo 2 he will need to depend on his spells to help him out greatly. Bone Armor does just that, absorbing damage while leaving the Necromancer unscathed.

Poison Dagger

Not a very wise spell to research unless you are using a dagger (which no one ever does). If you are using a dagger this spell would do wonders because it will increase the damage you do with the dagger by adding poison damage.

Corpse Explosion

The targeted corpse will explode damaging any and all nearby enemies greatly.

Bone Wall

If you have any minions do not even bother with this spell because your minions will, for some reason, destroy it. Other than that this is a great spell for making an escape or trapping enemies.

Poison Explosion

Same as Corpse Explosion but corpses explode into a cloud of poison. Since the poison cloud isnt that large this skill is hardly worth it.

Bone Spear

Bone Spear is the Necromancers main ranged attack. It will do a great amount of damage if you invest a lot of skill points into it and it also will go through many of the monsters.

Bone Prison

Same as with bone wall because of the fact that your minions will smash it right when they see it. Again if you dont have minions you can trap hero monster with it (that is until they destroy the prison).

Posion Nova

Same as Nova and Frost Nova that the Sorceress has Poison Nova creates a expanding ring of poison that infects all the monsters engulfed by it.

Bone Spirit

Bone Spirit is a projectile missile that seeks out and damages any target it finds.